Horizontal scroll on mouseMove - wide div in small

I'm trying to make a "line" of image thumbs, where it scrolls on mousemove. And I got it to work, but my problem now is that i wanted to make a "padding" on the sides so I doesn't have to have the mouse all the way out to the sides to see the first/last thumb. But I really really can't get it to work :/

This is the script I have now:

// MouseMove scrolling on thumbs
var box = $('.thumbs-block'),
    innerBox = $('.thumbs'),
    lastElement = innerBox.find('a:last-child');

var offsetPx = 100;
var boxOffset = box.offset().left;

var boxWidth = box.width() /* - (offsetPx*2)*/;
var innerBoxWidth = (lastElement[0].offsetLeft + lastElement.outerWidth(true)) - boxOffset /* + (offsetPx*2)*/;

scrollDelayTimer = null;
box.mousemove(function (e) {
    console.log('boxWidth: ' + boxWidth + '   innerBoxWidth: ' + innerBoxWidth + '   box.scrollLeft(): ' + box.scrollLeft());

    var mouseX = e.pageX;
    var boxMouseX = mouseX - boxOffset;

    if ((boxMouseX > offsetPx) && (boxMouseX < (boxWidth - offsetPx))) {
        var left = (boxMouseX * (innerBoxWidth - boxWidth) / boxWidth) /* - offsetPx*/;

        clearTimeout(scrollDelayTimer);
        scrollDelayTimer = setTimeout(function () {
            scrollDelayTimer = null;
            box.stop().animate({
                "scrollLeft": left
            }, {
                queue: false,
                duration: 500,
                easing: 'linear'
            });
        }, 10);
    }
});

There are some of the places I've tried adding the offset (commented out inline), some of it gets it working in one end but not the other :/

I'm pretty sure it's a problem in the math, but I can't figure out what I should do :/

Here's a jsFiddle: http://jsfiddle.net/6CJfs/1/

I hope I made my problem clear enough, not sure how to explain it otherwise, and hope someone can help :)

You script is not smooth, so I modified it completely (sorry :)
with a really simple approach:

LIVE DEMO

Super simple jQ:

$(function(){

    var $bl    = $(".thumbs-block"),
        $th    = $(".thumbs"),
        blW    = $bl.outerWidth(),
        blSW   = $bl[0].scrollWidth,
        wDiff  = (blSW/blW)-1,  // widths difference ratio
        mPadd  = 60,  // Mousemove Padding
        damp   = 20,  // Mousemove response softness
        mX     = 0,   // Real mouse position
        mX2    = 0,   // Modified mouse position
        posX   = 0,
        mmAA   = blW-(mPadd*2), // The mousemove available area
        mmAAr  = (blW/mmAA);    // get available mousemove fidderence ratio

    $bl.mousemove(function(e) {
        mX = e.pageX - this.offsetLeft;
        mX2 = Math.min( Math.max(0, mX-mPadd), mmAA ) * mmAAr;
    });

    setInterval(function(){
        posX += (mX2 - posX) / damp; // zeno's paradox equation "catching delay"    
        $th.css({marginLeft: -posX*wDiff });
    }, 10);

});

Add to CSS:

.thumbs-block {
    position:relative; /* THIS LINE */
    overflow: hidden;
    background: #ccc;
    margin: 0 5px;
    width: 714px;
    height:142px;      /* THIS LINE */
} 
.thumbs{ /* ALL */
  position:absolute;
  margin-left:0;      /* WILL BE CONTROLLED BY jQ */
}